Helical antenna feed element with switches to select end fire and backfire modes and circular polarization direction

Abstract

An antenna system capable of receiving electromagnetic radiation having either right or left helical polarization, and either vertical or horizontal linear polarization includes an energy concentrator which concentrates energy at a focal point. A helical antenna is arranged in the proximity of the focal point. A first switch switches the helical antenna to a backfire mode of operation and a second switch switches the helical antenna to an end fire mode of operation. A control mechanism controls the switches to select the nature of the polarization.

We claim: 
     
       1. An antenna system for receiving electromagnetic radiation from at least one direction and having at least one of right circular polarization, left circular polarizations, vertical linear polarization, and horizontal linear polarization, comprising: means for concentrating energy at at least one focal point;   a helical antenna including at least one helical feeder, each feeder having first and second ends arranged in the proximity of said focal point;   a first switch for switching said first end to a feeder line;   a second switch for switching said second end to said feeder line; and   control means for controlling said first and second switches in one of a first and second mode so that   in the first mode said first switch switches said first end to said feeder line whereby said helical antenna works in an axial backfire mode and receives radiation with a first circular polarization, and   in the second mode said second switch switches said second end to said feeder line whereby said helical antenna works in the axial endfire mode and receives radiation with a second circular polarization.   
     
     
       2. The antenna system of claim 1 wherein said first and second switches are simultaneously operated to put said helical antenna into a linear polarization mode of operation, and further including phase-shift means for selecting between horizontal and vertical linear polarization modes of operation. 
     
     
       3. The antenna of claim 1 wherein said first and second switches are diodes. 
     
     
       4. An antenna system for receiving electromagnetic radiation from at least one direction and having at least one of right circular polarization, left circular polarization, vertical linear polarization, and horizontal linear polarization, comprising: a first group of at least one helical feeder, each helical feeder having a first end and a second end with both ends of said feeder being connected by a fixed connection to a feeder line, each helical feeder having means for concentrating energy at at least one focal point;   phase-shifting means;   first control means for controlling said, phase-shifting means to select between said vertical and horizontal linear polarization modes of operation;   a second group of at least one helical feeder each helical feeder having a first end and a second end;   a first switch for switching said first end of each helical feeder of the second group to a feeder line;   a second switch for switching said second end of each helical feeder of the second group to said feeder line; and   second control means for controlling said first and second switches in one of a first and second mode so that   in the first mode said first switch switches said first end to said feeder line whereby said helical antenna works in the axial backfire mode and receives radiation with a first circular polarization, and   in the second mode said second switch switches said second end to said feeder line whereby said helical antenna works in the axial endfire mode and receives radiation with a second circular polarization.